Oring-448x227-cmprsdThe couplings used on Frigoboat component refrigeration systems are proprietary to Frigoboat and are designed for long and trouble-free service. Some time ago it was noticed that there was an increase in reports of leaking o-rings, and many were found to be caused by the coupling becoming excessively hot, damaging the rubber in the primary O-ring. Causes of excessive heat can be:

- badly fouled Keel Coolers;
- using a Keel Cooled system when out of the water and without temporary water cooling;
- inadequate ventilation of an air cooled unit;
- poor or restricted water flow in a pumped-water system.

The type of rubber in the O-rings was subsequently changed to better handle excessive heat, but damage may still result if any of the above situations are allowed to prevail.

Cap tube location moisture issueCap tube location blockage issueAll compression refrigeration systems depend on some device to separate the high and low pressure sides of the system. In a capillary (cap) tube system, this is the capilliary tube itself, which, as the name implies, has an extremely small micro-bore at its center that is less than the diameter of a needle.

There are two main issues that can occur with cap tubes: a particle blockage at the high pressure end near the compressor (picture on the left), and a moisture, wax, or oil problem at the other next to the evaporator (picture on the right). The Guide below describes the symptoms and recommended remedies for cap tube problems.

Capillary Tube Troubleshooting Guide


I’ll try not to get too technical on this subject, but there are some basic principles that you need to know before we get going. Firstly, we won’t be talking about hot and cold too often. It will be all heat, just at different temperatures above absolute zero (-460 deg F).
Next, we will be working in a unit of heat measurement known as a British Thermal Unit or Btu, and this is defined as the amount of heat required to raise or lower 1 pound of water 1 degree Fahrenheit.
Also it is important to remember that heat travels in one direction only; from a warm, high temperature area to a lower temperature area, and that we don’t “make cold”, we simply remove heat from one area and transfer it to somewhere else.

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